Generally, a stabilizer control device for the vehicle applies an appropriate rolling moment to a vehicle body, while the vehicle is traveling and making a turn, by actuating a stabilizer so that the rolling movement of the vehicle body is reduced or controlled.
A device described in JP2000-71739A controls an effect of the stabilizer for changing an apparent torsional rigidity of the stabilizer by driving and controlling an actuator in accordance with a level of a turning that the vehicle makes. Specifically, a thrust of an electromagnetic linear actuator is calculated on the basis of signals outputted from sensors, and a target electric current value is set by converting the thrust into an electric current value. Thus, PID control is executed.
A stabilizer described in JP2002-518245A has halves of a stabilizer bar, a first stabilizer bar and a second stabilizer bar, and an electromechanical turning actuator that is provided between the first and second stabilizer bars. Specifically, the electromechanical turning actuator used for generating an initial stress torque is comprised of three basic elements; an electric motor, a reducing gear device and a brake. The brake is provided between the electric motor and the reducing gear device. In this configuration, the torque generated by the electric motor is converted by means of the reducing gear device into another torque required for generating for the initial stress for the stabilizer. The first stabilizer is supported by a bearing and directly connected to a housing of the electromechanical turning actuator, and the second separated stabilizer is also supported by a bearing and connected to the reducing gear device at an output end (high-torque end) thereof.
Various types of motors can be used for the electric motor provided at the actuator described in JP2002-518245A, however, a brushless motor is particularly suitable for driving the actuator.
According to a brushless motor described in JPH8-228496A, a phase switching signal pattern is switched by a phase switching control means in accordance with a change of an output that is outputted by a rotation sensor for detecting rotations of a motor shaft, a phase switching signal is outputted to the switching element from the phase switching control means in accordance with the phase switching signal pattern, and then electric current is supplied to an exciting coil by driving the switching element in accordance with the phase switching signal.
Further, according to another brushless motor described in JPH7-40849A, a motor brake pattern is set as a phase switching signal pattern. Such motor brake pattern is described as L, L, L, H, H, H, in which L means a low-level signal, and H means a high-level signal.
Furthermore, a motor control device described in JP2005-33932A executes, when a power supplied to the motor is stopped, a process in order to deal with a torque generated by the motor.
When the drive of AC motor is stopped, if a rotational speed of the AC motor inputted by an input means is greater than a first rotational speed, the motor control device controls all elements in the first switching element group or the second switching element group so as to be in a conducting state, and the motor control device controls all elements in the other of the first switching element group or the second switching element group so as to be in a non-conducting state.
On the other hand, if a rotational speed of the AC motor inputted by the input means is less than a second rotational speed, the motor control device controls all elements in the first switching element group and the second switching element group so as to be in a non-conducting state.
When the brushless motor described in JPH8-228496A is used for the actuator described in JP2002-518245A, an actual angle (or an actual torque) is controlled so as to be close to a target angle (or target torque) by switching the rotating direction of the motor without supplying power to the brushless motor. Thus, the stabilizer can be controlled.
However, it is confirmed that torque fluctuations (vibrations) are generated on the basis of a characteristic of the stabilizer control device when the rotating direction is switched. It is also confirmed that such fluctuations make noise.
Specifically, as shown in FIG. 9, a dashed line indicates a target angle, and a solid line indicates an actual angle. For example, when a value of the actual angle at a certain point becomes lower than a value of the target angle, a rotating direction of the motor is switched without supplying electric current to the brushless motor as shown in a middle section of FIG. 9, and then torque fluctuations (vibrations) are generated right after the rotating direction is switched to a counterclockwise direction (CCW), and such fluctuations make noise. In FIG. 9, CW indicates a clockwise direction rotation (right rotation), and CCW indicates a counterclockwise direction rotation (left rotation).
A need thus exists to provide a stabilizer control device, which has a brushless motor in order to control a torsional force generated at the stabilizer, wherein the rolling movement of the vehicle is appropriately reduced, and noise is reduced.